Preparation of two-sided mosaic screen



Dec. 15, 1953 G. K. TEAL PREPARATION OF TWO-SIDED MOSAIC SCREEN Fil edDec. 29, 1948 F IG.

wvs/vron G. K TEAL y Dec. 15, 1953 G. K. TEAL 2,662,852

PREPARATION OF TWO-SIDED MOSAIC SCREEN Filed Dec. 29, 1948 sSheets-Sheet 2 FIG. /3

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EVAPORATI' lNVENTOR 6. K. 7' EAL BY 7 71 5. 6/145 ATTORNEY Dec. 15, 1953G. K. TEAL 2,662,852

PREPARATION OF TWOSIDED MOSAIC SCREEN Filed Dec. 29, 1948 3 Sheets-Sheet3 FIG. /7

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I L l '1 P, mam cums ALUMINUM ELECTRODE INVENTOR G. A. TEAL A?! J? MagATTORNEY Patented Dec. 15, i953 PREPARATION OF TWO-SIDED MOSAIC SCREENGordon K. Teal, Summit, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 29, 1948,Serial No. 67,917

2 Claims.

This invention relates to electro-optical devices and more specificallyto methods of making target or screen structures for use in televisiontransmitter tubes.

It has long been recognized in the development of electron camera tubesfor generating picture signals at a television transmitting station thatthere are many advantages in projecting an elec tron image of the objectfor transmission onto one side of the screen of the tube and scanningthe opposite side of the screen with a cathode ray beam formed in thetube. An example of a camera tube employing such a two-sided target orscreen is the so-called image orthicon tube, described in an articleentitled The Image OrthiconA sensitive Television Pick-up Tube by AlbertRose, Paul K. Weimer and Harold B. Law, appearing in the July 1946 issueof the Proceedings of the I. R. E., beginning on page 424. The two-sidedtarget makes possible the separation of charging and dischargingprocesses so that the sensitizing procedures and electric fieldsappropriate to each can be incorporated in the tube without mutualinterference. The target must conduct charges between its two sides orsurfaces but not along either surface. Moreover, it should have aconducting element therein or nearby to act as the common capacitorplate for the separate picture elements. It has been found verydiflicult to construct satisfactory commercial targets of this type.

It is an object of the present invention to provide novel and improvedmethods for making two-sided electron camera tube targets which have alarge number of discrete conducting elements per square inch.

In an exemplary method of making a two-sided mosaic target for cameratubes and the like in accordance with the invention, Ell aperturedmetallic screen is formed by pressing a number of very hard, smallparticles into a thin metal film; the apertured thin film is thickened,the resulting screen is electrolytically polished, its apertures arefilled with silver oxide by a sputtering process in which silver isbombarded in oxygen with high voltage discharges, and the silver oxideis then reduced to silver. This method produces a two-sided metellicmosaic screen havin a multiplicity of insulated metallic plugs therein.

The invention will be more readily understood by referring to thefollowing description taken in connection with the accompanying drawingsforming a part thereof in which:

Figs. 1 to 6, inclusive, illustrate various steps 2 in a method offorming an apertured metallic screen in accordance with the invention;

Figs. 7 to 11, inclusive, illustrate steps in the process ofelectrolytically polishing the screen shown in Fig. 6;

Figs. 12 to 16, inclusive, illustrate a method of increasing the numberof holes in the screen shown in Fig. 11;

Figs. 17 to 20, inclusive, illustrate a method of filling the aperturesin the screen shown in Fig. 16 with insulated plugs;

Fig. 21 is a top view of a schematic represen tation in greatly enlargedform of a portion of a target made in accordance with the invention;

Fig. 22 is a sectional side view of portions of such target; and

Figs. 23 shows apparatus used in carrying out the invention.

Referring more specifically to the drawings, Figs. 21 and 22 show, byway of example for purposes of illustration, portions of a two-sidedmosaic target 3!] suitable for use in certain television transmittingtubes, such'as, for example, the image orthicon type of tube brieflyreferred to above. It will be understood that Figs. 21 and 22 are merelyschematic showings and the same applies to the other figures in thedrawings. Target 30 comprises a thin metallic screen 53 of a suitablemetallic material having a large number of holes to the linear inch, e.g., four hundred per inch or more. One surface, such as the top surfacein Fig. 22, and the interiors of all the apertures in the screen 53 arecoated with an insulating material 54. The interiors of all theseapertures are filled with metallic plugs 51A. Successive steps in thepreparation of the screen or target 30 will be easily understood byreferring to Figs. 1 to 20, inclusive, in some of which for simplicityin the drawings, the structure around one aperture only has been shown.

The first six figures of the drawings illustrate schematically a methodof forming a metallic screen having a number of apertures therein. Fig.1 shows a thin conducting layer 40 of platinum or other suitablematerial which is evaporated, sprayed, sputtered or otherwise depositedon a wax block 4|. Very small particles of uniform diameter areinsufflated upon the surface of the film 40. These particles 42 may beany hard particlefsuch as diamond, sapphire, iron, nickel or othersolid. Fig. 2 shows these particles on the conducting film 40.

As shown in Fig. 3, the particles 42 are pressed into the metal film 40with a roller or a smooth fiat or curved plate. This breaks small areasof 3 the metal 40 away from the main part of the conducting film leavingthereby a perforated screen on the surface of the wax. Small areas 43 ofthe screen are pressed into the wax block 4| and, as shown, angularprojections 41A extend downward from around each perforation.

If the particles 42 are conductors such as iron or nickel, they may bedissolved with nitric or hydrochloric acids. If the particles 42 areinsulating particles this step can be omitted.

As thick a coat of nickel is applied to the platinum screen 40 as ispossible without closing up the holes 44. Any suitable method, such aselectroplating, can be used. The coating 45 is shown in Fig. 5.

Let it be assumed that an enlarged side view of one of the apertures 44and of its surrounding metal is shown in Fig. '7, and a largecross-section of the aperture 44 is shown in Fig. 8. It is obvious thatthe actual aperture 44 is by no means as smooth as is represented inFig. 7. It has been shown in this manner merely for convenience andsimplicity in the drawings. It will be noted that the metal screen 46shown in Fig. '7 has angular projections 41A around the hole and alsosmall irregular projections 48A. The screen 46 is then electrolyticallypolished by making it the anode in a solution of sulfuric acid and water(120 cc. H2804 to 80 cc. H2O) at a high current density. This rounds ofisome of the projections and dissolves part of the nickel screen asindicated in Figs. 9 and 10 which otherwise correspond to Figs. 7 and 8,respectively. A thin film of metal is then electroplated upon the screen46 and the polishing process is repeated and re-repeated as often asnecessary to give the smooth screen 46 shown in Fig. 11. It will benoted that in Figs. 7 to 11, inclusive, no attempt has been made to showthe various metal layers (such as, for example, layers 45 and 40) makingup the screen, it being shown for simplicity merely as a solid metalscreen 46.

Figs. 12 to 16, inclusive, illustrate a method of increasing the numberof holes in the screen 46. As shown in Fig. 12, the metal screen 46shown in Fig. 11 is placed upon and in intimate contact with a piece ofthin filter material 41, such as paper, and a metal, such as aluminum,or other solid is evaporated through the holes 44 in the screen. Thisgives a pattern of thin solid dots 43 over the entire surface of thepaper as indicated in Fig. 13. Obviously the dots are not perfectcircles as shown in Fig. 13 but are shown thus for simplicity in thedrawings.

The screen 46 is then shifted into position so that the holes 44 fall inthe positions indicated by the clear circles 49A in Fig. 14, and a solidis evaporated through the holes in the screen while it is in thisposition to produce new thin solid dots 49 (shown in Fig. 16).

The metal screen 46 is then removed and the filter paper 41 upon whichaluminum dots 48 and 49 have been superimposed is placed upon a filtercylinder 50 of sintered glass or glass containing a multiplicity ofcapillary holes, and a layer of silver oxide or copper oxide isdeposited upon the paper while vacuum is applied to the underside of thecylinder. The entire assembly is then placed in a reducing atmosphereand the silver oxide or copper oxide is reduced to silveror copper, thefilter paper being burned away during the reducing process. The aluminumdots 48 and 49 are now etched out of the holes with concentratedpotassium hydroxide solution giving a perforated metal screen havingtwice the number of holes possessed by the original screen.

The metal screen produced by the process illustrated by Figs. 12 to 15,inclusive, is now used in a repetition of this procedure to produce ametal screen having holes including those shown as 48 and 49 in Fig. 14and also those shown in the positions of the dotted circles 52 in Fig.16. This produces a screen shown as 53 in Fig. 17 which contains fourtimes the total number 01' holes as the screen shown in Fig. 12 andtwice the number 01' holes per linear inch as that shown in Fig. 12.

Figs. 17 to 20, inclusive, illustrate a method of filling the aperturesin the screen 53 with insulated metallic plugs. Referring now to Fig.1'7, the metal screen 53 is coated with insulating layer 54. This isobtained by evaporating a suitable substance such as cryolite on the topof the screen or by insufilating glass on the screen and then fusing itto give the coating 54. A uniform coating of beeswax, asphaltum or otheradhesive 55 is applied to a fairly thick stiff piece of metal or glass56. The adhesive is flowed on the metal or glass 55 by melting or by useof a solution of the adhesive in a solvent such as carbon tetrachloride.Evenness of spreading can be assured by spinning in a horizontal plane.The coated metal screen 53 is pressed onto the wax film 55 so that asmall amount 55A of the wax is pushed into each hole of the screen asshown in Fig. 1'7. Silver oxide 51 is then applied to the surface of theunit of Fig. 17 by bombarding silver in oxygen with high voltagedischarges. This can be accomplished in the apparatus shown in Fig. 23,wherein the unit 58 shown in Fig. 17 and represented schematically by arectangle in Fig. 23 is mounted in the path between a silver electrode59 and an aluminum electrode 60 in an oxygen atmosphere, and a source ofhigh D. C. voltage 5| is connected between the two electrodes. Because01' the oxygen atomsphere a. multiplicity of silver oxide particles 51is built up in the apertures of the unit 58.

The excess silver oxide is then wiped off, leaving the silver oxideplugs 51 in the holes of the screen 53 as shown in Fig. 19. The unit isthen heated up and the screen is removed from its supports.

The screen of Fig. 19 is then heated in hydrogen to reduce the silveroxide 51 to silver buttons 51A. Alternatively, it can be treated with aliquid reducing agent like one of those frequently used in photography,for example. This produces a screen one elemental portion of which isshown in Fig. 20 and another larger portion of which is shown, to asomewhat smaller scale, in Figs. 21 and 22.

Various alternative steps and procedures other than those mentionedabove are of course possible without departing from the spirit of theinvention, the scope of which is pointed out in the claims. Thedisclosed over-all process of making screens of the type shown in Figs.21 and 22 is claimed in the present application; the methods disclosedherein (Figs. 1 to 6, inclusive) of forming an apertured metal screen ofthe type shown in Fig. 6 are claimed in a copending divisionalapplication of the present inventor, Serial No. 123,873, filed October27, 1949; the methods disclosed herein of electrolytically polishingapertured metal screens (Figs. '7 to 11, inclusive) are claimed in acopending divisional application of the present inventor, Serial No.123,874, filed 0ctober 27, 1949; the methods disclosed herein o1increasing the number of holes in aperture metal screens (Figs. 12 to16, inclusive) are claimed in another copending divisional applicationof the present inventor, Serial No. 123,875, filed October 27, 1949,issued as patent number 2,596,617 on May 13, 1952; and the sputteringmethod disclosed herein and the apparatus used therefor (Figs. 17 to 20,inclusive, and 23) are claimed in still another copending divisionalapplication of the present inventor, Serial No. 123,876, filed October27, 1949.

What is claimed is:

l. The method of forming a two-sided mosaic screen or target comprisingthe steps of placing a large number of tiny hard particles on a metallayer, pressing the particles into and through said metal layer therebyforming a large number of apertures in the layer, applying a metalcoating to said layer leaving a thickened apertured screen which hassharp metallic projections therein, electrolytically polishing thethickened screen to reduce said projections, electroplating said layerto increase the thickness thereof, insulating the inner surfaces of theapertures in the metal layer and forming metallic buttons in saidinsulated apertures.

2. The method of forming a two-sided mosaic screen or target comprisingthe steps of placing a large number of tiny hard particles on a metallayer, pressing the particles into and through said 6 metal layerthereby forming a large number of apertures in the layer, applying ametal coating to said layer leaving a thickened apertured screen whichhas sharp metallic projections therein, electrolytically polishing thethickened screen to reduce said projections, electroplating said layerto increase the thickness thereof, repeating said electrolytic andelectroplating steps a plurality of times until smooth apertures in ametal layer of desired thickness are produced, insulating the innersurfaces of the apertures in the metal layer 'and forming metallicbuttons in said insulated apertures.

I GORDON K. TEAL.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,792,197 Stresan Feb. 10, 1931 2,103,623 Kott Dec. 28, 19372,163,480 Burkhardt et al. June 20, 1939 2,175,701 Rose Oct. 10, 19392,225,733 Beebe Dec. 24, 1940- 2,352,968 Orton July 4, 1944 2,412,058Pfeil Dec. 3, 1946 2,496,299 Mansfield et al Feb. 7, 1950 2,496,961Schneider Feb. 7, 1950 2,596,617 Teal May 13, 1952 2,596,618 Teal May13, 1952

1. THE METHOD OF FORMING A TWO-SIDED MOSAIC SCREEN OR TARGET COMPRISINGTHE STEPS OF PLACING A LARGE NUMBER OF TINY HARD PARTICLES ON A METALLAYER, PRESSING THE PARTICLES INTO AND THROUGH SAID METAL LAYER THEREBYFORMING A LARGE NUMBER OF APERTURES IN THE LAYER, APPLYING A METALCOATING TO SAID LAYER LEAVING A THICKENED APERTURED SCREEN WHICH HASSHARP METALLIC PROJECTIONS THEREIN, ELECTROLYTICALLY POLISHING THETHICKENED SCREEN TO REDUCE SAID PROJECTIONS, ELECTROPLATING SAID LAYERTO INCREASE THE THICKNESS THEREOF, INSULATING THE INNER SURFACES OF THEAPERTURES IN THE METAL LAYER AND FORMING METALLIC BUTTONS IN SAIDINSULATED APERTURES.